The invention relates generally to plasma processing reactors. In particular, the invention relates to controlled texturing of a domed roof in an etch reactor.
A new class of plasma reactors has recently emerged for processing of semiconductors wafers during the fabrication of integrated circuits. These reactors include an RF inductive coil positioned in back of a dome or roof overlying the wafer being processed. An RF power source is connected to the coil to couple inductive energy into the plasma reaction chamber and to create a plasma source region remote from the wafer being process. Because of the separation between the wafer and the plasma source region, some of these reactors are sometimes referred to as having a decoupled plasma source (DPS). Hanawa et al. disclose a number of domed configurations in U.S. Pat. No. 5,753,044. One of these designs has been incorporated into the DPS Etch Reactor available from Applied Materials, Inc. of Santa Clara, Calif. primarily for etching metal and polysilicon. A similar design has been commercially applied to high-density plasma (HDP) chemical vapor deposition. Collins et al. in U.S. Pat. No. 6,024,826 describe a related design having a planar roof and configured for etching oxide.
Shih et al. disclose the details of the chamber wall configuration for the DPS Etch Reactor in U.S. patent application Ser. No. 08/770,092, filed Dec. 19, 1996, issue fee paid.
The chamber, illustrated in the cross-sectional view of FIG. 1, includes an arcuate ceramic dome 10 sealed to a grounded metal chamber wall 12, which is surfaced coated with boron carbide. A pedestal electrode 14 for supporting a wafer 16 to be etched is vertically raisable to seal to the bottom of the chamber wall 12 after the wafer 16 has been placed on the pedestal 14. Unilllustrated gas supply ports and a vacuum pumping port penetrate the chamber wall 12 above the sealed pedestal 14. The lower part of the chamber below the pedestal 14 is not illustrated, and the cited patents should be consulted for its details.
An inductive coil 20 is wrapped around the outer portions of the arcuate dome 10. An RF power supply 22 couples RF electrical energy into coil 20 and thence through the ceramic dome 10 into the interior of the chamber to create a plasma source region adjacent to the dome 10. A second RF power supply 24 electrically biases the pedestal electrode 14 through a capacitive coupling circuit 26 to allow a negative DC self-bias to develop on the pedestal electrode 14 relative to the plasma within the chamber. The pedestal DC bias controls the energy of ions attracted from the plasma across the plasma sheath to thereafter strike the wafer 16. One advantage of a decoupled plasma source is that the wafer bias can be controlled independently of the plasma source power.
Because electromagnetic radiation is transferred through the dome 10, the dome must be made of electrically insulating material to act as a dielectric window to allow the coil antenna 10 to couple RF energy into the plasma source region within the chamber. For chlorine-based etching of metals, for example, using BCl3 to etch aluminum, ceramic alumina (Al2O3) is the typical dome material.
A recurring problem with reactor chamber walls is that, even in an etching environment, residue tends to form on the walls resulting from byproducts of the etching process. In a BCl3 plasma, a brownish gold to brown film quickly forms. The residue film adhering to the chamber wall often does not inherently present major problems. However, when the film builds up to a significant thickness, portions of it are likely to flake off and fall into the processing area of the chamber. Any such particle that falls onto the wafer is likely to produce a failure or reliability problem in the integrated circuit being fabricated. In view of decreasing feature sizes of integrated circuits, a single particle as small as 0.1 xcexcm can cause a failure. The residue particle problem seems to be particularly severe for ceramic domes used as dielectric windows for coil antennas. The source coil is intended to couple large amounts of energy into the chamber and hence is often operated at high power levels. Inevitably, a substantial fraction of the RF energy is thermally dissipated into the dome. However, the coil is only intermittently operated as wafers are cycled into and out of the chamber, and a ceramic is usually a poor thermal conductor. As a result, the dome material is subjected to repeated and significant temperature swings, resulting in repetitive cycles of thermal expansion and contraction of the dome. The thermal effects are largest in the areas immediately adjacent to the wraps of the coil. Under these conditions, the residue film is more likely to flake and produce deleterious particles.
One method to reduce the particle problem from the dome is to periodically replace it or at least clean it in situ before a critical film thickness is deposited. At a minimum, cleaning imposes significant system downtime and requires manual involvement of technicians.
Accordingly, it is greatly desired to either reduce the thickness of the film residue or to increase its adhesion to the chamber wall so that the mean time between chamber cleaning or replacement can be increased. It is further desired that such improvements be obtainable with conventional ceramic materials.
The invention may be summarized as a wall of a plasma processing chamber having formed on its interior side at least a macroscopic texturing having a size of between about 0.5 and 5 mm, for example, concentric triangular grooves. The macroscopic texturing increases the effective surface area of the dome on which residue film is deposited.
Preferably, a second, microscopic level of texturing is superimposed on the first level. The macroscopic texturing has a size of at least ten and preferably at least 100 times the size of the microscopic texturing. The microscopic texturing improves the adhesion of the residue film.
The invention is particularly useful for ceramic walls, and most particularly for ceramic domes acting as dielectric windows in plasma processing reactors for passing electromagnetic radiation from an RF coil positioned outside of the dome.
The texturing may be accomplished on the green form used in sintering the ceramic member. Grooves or other macroscopic features may be machined into the green form.
Bead blasting may be used to roughen the surface of the macroscopic features. Preferably, firing occurs after the bead blasting.